I agree with you regarding photography in museums. If one is discreet and respectful and quiet, I don't see how anyone would have a problem.
Over the past six months I have visited the National Gallery in Washington, D.C., The Met in NY, the Tretyakov, Hermitage, Russian museums and endless churches and palaces.
In the states it was never a problem taking photos, as long as there was no flash used.
In Russia it was, as usual these days, wild west capitalism. Almost everywhere I went (and I went almost everywhere, or so it seemed), visitors had the option of paying up to 600R to take interior photos or video. The only place I encountered where photography was not allowed at all was the Amber Room, and of course, churches, though I personally know people (Russians, anyway) who have videotaped or photographed inside churches, but not during a service.
Over all, it seems that while some regard photography in museums as impolite, in many major museums it is officially acceptable, though many times conditional.